ImportError: Twisted requires zope.interface 3.6.0 or later: no module named zope.interface

Question

I am trying to build a web scraper (http://doc.scrapy.org/en/0.24/intro/tutorial.html#intro-tutorial), but when I am trying to launch the crawler, I am getting this error:

Traceback (most recent call last):
  File "/Applications/anaconda/bin/scrapy", line 7, in <module>
    from scrapy.cmdline import execute
  File "/Applications/anaconda/lib/python2.7/site-packages/scrapy/__init__.py", line 50, in <module>
    from twisted import version as _txv
  File "/Applications/anaconda/lib/python2.7/site-packages/twisted/__init__.py", line 53, in <module>
    _checkRequirements()
  File "/Applications/anaconda/lib/python2.7/site-packages/twisted/__init__.py", line 37, in _checkRequirements
    raise ImportError(required + ": no module named zope.interface.")
ImportError: Twisted requires zope.interface 3.6.0 or later: no module named zope.interface.

I checked my installations with pip freeze, and it seems that I have it installed:

zope.interface==4.1.1

What could be the issue here?